This function solves a USL model using non linear regression with least
squares. It uses the function nls with the "port"
algorithm to perform the calculation. All restrictions of the algorithm
apply.
usl.solve.nls(model)A list containing three elements: the model coefficients alpha, beta and gamma.
A data frame with two columns containing the values of the predictor variable in the first column and the values of the response variable in the second column.
usl